Friedrich Rudolf Klein (24 November 1885 – 29 May 1955), better known as Rudolf Klein-Rogge, was a German film actor, best known for playing sinister figures in films in the 1920s and 1930s as well as being a mainstay in director Fritz Lang's Weimar-era films. He is probably best known in popular culture, particularly to English-speaking audiences, for playing the archetypal mad scientist role of C. A. Rotwang in Lang's Metropolis and as the criminal genius Doctor Mabuse. Klein-Rogge also appeared in several important French films in the late 1920s and early 1930s.